1. Field of the Invention
The invention is directed to a Vibration damper comprising a cylinder in which a piston fastened to a piston rod executes a translational and a rotational movement relative to the cylinder.
2. Description of the Related Art
In a vibration damper, the piston executes an axial relative movement relative to the cylinder. As a rule, a piston nut causes a pre-loading between the piston and the piston rod so that the connection between the piston and piston rod is not loosened.
Particularly in vibration dampers on articulated axles, the piston, together with the piston rod, also carries out a rotational relative movement relative to the cylinder. The piston can also execute a rotational relative movement relative to the cylinder in vibration dampers arranged at an inclination to the swiveling axis of an axle part. In this way, it can come about that the friction force between the inner wall of the cylinder and the piston exerts a loosening torque on the piston nut.
Particularly in vibration dampers for upscale vehicle types, bearings are provided which allow a relative movement of the piston rod relative to the vehicle body, as is disclosed in DE 37 16 819 A1, for example. The problem of loosening of the piston does not arise in vibration dampers of this kind.
As an alternative measure, for example, piston nuts are used whose thread pitch diverges slightly from a fastening thread of the piston rod. In this connection, reference is had to DE 34 29 473 A1, for example.
DE 101 61 801 A1 suggests a deliberate deformation of the piston nut as a solution for securing the piston. Further, self-locking nuts are also known.
In principle, the problem of loosening described above arises not only when pistons are secured by screwing, but also in pistons that are riveted to the piston rod. The method for fastening the piston to the piston rod is secondary, since every rotational movement of the piston relative to the piston rod shortens the life of the vibration damper.